1. Field of the Invention
The present invention relates to a manually controlled lifting device having a pneumatic lifting drive, a lifting member connected to the drive and a load-carrying means arranged at the end of the lifting member. A pneumatic switch is integrated in a pressure line connecting a compressed-air source to a pressure space of the lifting drive. The pneumatic switch connects the pressure space of the lifting drive to the compressed-air source in one position and to a vent device in another position.
2. Description of the Related Art
A number of manually controlled lifting devices have been disclosed, in which the lifting member in the simplest case is formed by a rope. In other cases, the lifting member is formed, for example, by the jib of a manipulator, a scissors system of a lifting platform or the like. All of these designs exhibit the adverse phenomenon that the lifting and lowering speed greatly depends on the load to be moved. The reason for this lies in the basic relationship p xc2x7V= const. i.e. for a given lift, twice the air quantity at double the load has to be supplied to the pressure space of the lifting drive, a factor which results in a correspondingly reduced lifting speed. This may lead to unpleasant and even dangerous operating states, for example, when the lifting member is raised in an unloaded manner. In particular, if the lifting member is designed as a virtually massless rope, this leads to the rope shooting up abruptly, which causes the feared rope whip, which is exceptionally dangerous for the operator. A similar phenomenon occurs during the lowering of the load, if, during venting of the pressure space of the lifting drive, the load is lowered at high speed and strikes a base.
The object of the present invention, is to provide a lifting device with little extra technical outlay, which achieves at least approximately the same lifting and lowering speeds within the entire working range and irrespective of the load to be moved.
According to the present invention, this object is achieved in that a flow-control device lying in the load flow is integrated between two load-transmitting components. The flow control device is simultaneously connected in a compressed-air line between the pneumatic switch and the pressure space of the lifting drive. Under the action of the load, the flow control device acting on the load-carrying means, automatically varies the cross section of flow of the compressed-air line in such a way that:
a) during a lifting operation, a larger cross section of flow is set during high load than during low load, and
b) during a lowering operation, a smaller cross section of flow is set during high load than during low load.
By these measures, a virtually identical lifting and lowering speed is always achieved irrespective of the load to be moved.
In order to realize this measure in terms of design, the flow-control device
a) may contain two adjustable restriction valves which are connected in parallel with one another and with which:
b) a respective check valve is connected in series, and with
c) a restriction valve which increases the restriction cross section during increasing load being assigned to the check valve which opens in the direction of flow from the pneumatic switch to the pressure space, and
d) a restriction valve which reduces the restriction cross section during increasing load being assigned to the check valve which opens in the opposite direction of flow.
This combination of two adjustable restriction valves and two check valves ensures that dangerous rapid lifting and lowering operations described above are reliably avoided.
The restriction valves may be directionally controlled in such a way that, when their axial length changes, a corresponding change in the restriction effect occurs. Such restriction valves may be designed in such a way that a spring-loaded actuating pin projects from an axially extending housing, during the axial displacement of which actuating pin the restriction cross section in the housing interior is changed.
In order to achieve as compact a design as possible, it may be expedient to combine the two restriction valves, or alternatively both restriction valves and both check valves, to form a common construction unit.
The two restriction valves may be accommodated in a common outer housing in such a way that they bear with their two axial ends against the inner surfaces of two walls, opposite one another, of the outer housing. The mutual distance apart of which is variable under elastic deformation, on the outer surfaces of which walls tension or compression forces from load-transmitting components act.
The load-dependent elastic deformation of the outer housing thus acts on the restriction valves in such a way that a virtually identical lifting and lowering speed is set in all operating states.
The object of the present invention, is to provide a lifting device with little extra technical outlay, which achieves at least approximately the same lifting and lowering speeds within the entire working range and irrespective of the load to be moved.
According to the present invention, this object is achieved in that a flow-control device lying in the load flow is integrated between two load-transmitting components. The flow-control device is simultaneously connected in a compressed-air line between the pneumatic switch and the pressure space of the lifting drive. Under the action of the load, the flow control device acting on the load carrying means, automatically varies the cross section of flow of the compressed-air line in such a way that:
a) during a lifting operation, a larger cross section of flow is set during high load than during low load, and
b) during a lowering operation, a smaller cross section of flow is set during high load than during low load.
By these measures, a virtually identical lifting and lowering speed is always achieved irrespective of the load to be moved.
In order to realize this measure in terms of design, the flow-control device:
a) may contain two adjustable restriction valves which are connected in parallel with one another and with which
b) a respective check valve is connected in series, and with
c) a restriction valve which increases the restriction cross section during increasing load being assigned to the check valve which opens in the direction of flow from the pneumatic switch to the pressure space, and
d) a restriction valve which reduces the restriction cross section during increasing load being assigned to the check valve which opens in the opposite direction of flow.
This combination of two adjustable restriction valves and two check valves ensures that dangerous rapid lifting and lowering operations described above are reliably avoided.
The restriction valves may be directionally controlled in such a way that, when their axial length changes, a corresponding change in the restriction effect occurs. Such restriction valves may be designed in such a way that a spring-loaded actuating pin projects from an axially extending housing, during the axial displacement of which actuating pin the restriction cross section in the housing interior is changed.
In order to achieve as compact a design as possible, it may be expedient to combine the two restriction valves, or alternatively both restriction valves and both check valves, to form a common construction unit.
The two restriction valves may be accommodated in a common outer housing in such a way that they bear with their two axial ends against the inner surfaces of two walls, opposite one another, of the outer housing. The mutual distance of the walls is variable under elastic deformation, on the outer surfaces of which walls tension or compression forces from load-transmitting components act.
The load dependent elastic deformation of the outer housing thus acts on the restriction valves in such a way that a virtually identical lifting and lowering speed is set in all operating states.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.